1. Field of the Invention
This invention relates to a plate clamping apparatus for a leaf-type printing machine, and more particularly to a plate clamping apparatus of this kind which can facilitate plate clamping and stretching operations.
2. Description of the Prior Art
When a given printing job has been completed and before the next one is to be done, it is necessary to replace the plate or master on the peripheral surface of the plate roller. Such plates are generally replaced by a manual operation in a procedure that will be explained hereinafter with reference to FIGS. 1 to 4.
In FIG. 1 there is illustrated a plan view of a conventional manual plate clamping apparatus 1, for a leaf-type printing machine. The clamping apparatus 1, is accommodated in a recess axially formed in a plate roller 2.
The clamping apparatus 1, includes, as its main constituents, a top side clamp 4 and a bottom side clamp 5 for attaching the plate 19 and a plate stretcher 12 provided for stretching the plate 2 wound on the plate roller 2. The top side clamp 4 has lower tooth 20 and upper tooth 21, the latter being divided into four parts. A spring 22 and a top side cam shaft 6 are interposed between the lower and upper teeth 20 and 21. The teeth 20 and 21 and the cam shaft 6 are adjustably bolted by a spherical-headed bolt 23. The lower tooth 20 is provided with a bolt 24 for fine adjustment.
The bottom side clamp 5 includes a lower tooth 25 and an upper tooth 26, the latter being divided into four parts. A spring 2 and a bottom side cam shaft 7 are interposed between the teeth 25 and 26. The lower and upper teeth 25 and 26 and the cam shaft 7 are adjustably bolted by a spherical-headed bolt 28. The lower tooth 25 is provided with a bolt 29 for fine adjustment.
Further, a plate stretching cam shaft 13 is disposed between the bottom side lower tooth 25 and a groove 30 formed on the plate roller 2. Also, a spring 31 is inserted between the top side lower tooth 20 and the bottom side lower tooth 25. Such arrangement allows the tip of the fine adjustment bolt 29 to be in contacted with the plate stretching cam shaft 13.
In the conventional manual plate clamping apparatus constructed as described above, the plate 19 is attached and removed, as shown in FIGS. 2 and 3, by manually rotating the cam shafts 6 and 7 with tools (not shown) which are suspended on tool suspenders 32 and 33 arranged at an axially central portion of the cam shafts 6 and 7, respectively.
Further, the plate is stretched by manually rotating the plate stretching cam shaft 13 with a tool (not shown) suspended on an end portion of the cam shaft 13.
Winding the plate 19 on the peripheral surface of the plate roller 2 is explained in detail with reference to FIGS. 2 to 4.
First, the plate clamping apparatus 1' is placed a condition shown in FIG. 2. Specifically, tools are suspended on the tool suspenders 32 and 33 to direct notches 6a and 7a of the cam shaft 6 and 7 in the upward direction. The top side and bottom side upper teeth 21 and 26 are thus lifted by the bracing force of the springs 22 and 27, respectively, with the spherical-headed bolts 23 and 28 as fulcrum. A gap is consequently formed between the top side lower and upper teeth 20 and 21 and the bottom side lower and upper teeth 25 and 26. Further, a tool is hooked on a peg 34 to direct a notch 13a of the plate stretching cam shaft 13 toward the top of the fine adjustment bolt 29. The spring 31 urges the top of the bolt 29 to the cam shaft 13, whereby the bottom side clamp 5 is biased on the left side (see FIG. 2).
Next, the plate roller 2 is rotated to a position which facilitates attachment of the plate 19 to the top side clamp 4. Then, the top side edge 19a of the plate 19 is inserted between the lower and upper teeth 20 and 21, and the cam shaft 6 is manually rotated in the clockwise direction to close the upper tooth 21, thereby clamping the top side edge 19a.
When the top side edge 19a has been clamped by the top side clamp 4, the plate roller 2 is rotated to a position which facilitates attachment of the plate 19 to the bottom side clamp 5, while the plate is closely contacted on the peripheral surface of the plate roller 2. In this condition, the bottom side edge 19b is inserted between the lower and upper teeth 25 and 26, and then the cam shaft 7 is manually rotated in the counterclockwise direction to close the upper tooth 26, thereby clamping the bottom side edge 19a (see FIG. 3).
When both edges 19a and 19b have been clamped by the top and bottom side clamping portions 4 and 5, the plate stretching cam shaft 13 is manually rotated in the counterclockwise direction to move the bottom side clamp 5 to the right side of FIG. 14 as well as closely contact the plate 19 on the peripheral surface of the plate roller 2, thereby completing attachment of the plate 19 on the peripheral surface of the plate roller 2 (see FIG. 4).
Removal of the plate 19 may be effected in the reverse order of the above mentioned plate attaching procedure.
As described above, manual replacement of the plate 19 takes a long time, particularly in the case of a multicolored printing machine, thus presenting a problem in that the working ratio of the leaf-type printing machine cannot be improved.
Plate clamping and plate stretching operations, within a plate replacement procedure, are carried out by an operator who is required to manipulate tools in a small area. As a result, the operator has to carry out dangerous work with a bad posture. To solve such problems, there are known Japanese Patent Prepublications Nos. 67051/1987 (Prior art 1) and 164539/1987 (Prior art 2) and Japanese Utility Model Prepublication No. 47134/1988 (prior art 3).
Prior art 1 provides a plate stretching operation without the necessity of manual operation. However, the position at which the plate is to be stretched is determined by the position at which a coupler and a drive for moving the coupler are attached to a frame. It is thus difficult to select a proper position at which the plate clamping operation can be easily carried out.
Prior Art 2 eliminates a manual operation only in the plate clamping procedure while the plate stretching operation still requires a manual operation. Furthermore, depending upon the installed position of the apparatus, the plate must be clamped at a fixed position, making it quite difficult to freely adjust the working position in order to facilitate the plate clamping operation when the top end 19a of the plate 19 is inserted between the top side lower and upper teeth 20 and 21 as well as when the bottom end 19b is inserted between the bottom side lower and upper teeth 25 and 26.
Prior Art 3 can only eliminate the manual operation in the plate clamping procedure, similar to Prior Art 2. The plate stretching procedure must be manually carried out. Also, the working position is fixed depending upon the installed position of the automatic plate clamping apparatus. Consequently, it is difficult to freely adjust the working position in order to facilitate the plate clamping procedure when the top end 19a is thereafter inserted between the upper teeth 20 and 21 as well as when the bottom end 19b is inserted between the lower and upper teeth 25 and 26, as described above.